Serious rennies will want historical costuming stuff. We can be a tough crowd, but we'll also drop a lot of money on the right item. Costumy stuff needs to be, or at least look like, made from natural and historically correct items - leather rather than pleather, no big glued-on craft jewels, etc.
If you want to reach out to the more casual faire goers, I think you can't go wrong making something inexpensive and "blingy" for kids. Parents will be busy telling their kids that they can't have $200 genuine steel swords, but they'll buy a $4 foam sword. Little girls like princessy stuff. A lot of the women will walk around all day in flower wreaths and regular clothes, just because you don't buy flower wreaths from street vendors in "the real world."
I always shop for fancy scented soaps. Some of the gourmet shops do great - candies, preserves, etc. - by setting out samples. The soap shop I like best even has samples! They put small soap pieces in a big basket, and I woman stands out front and yells, "Get your soap sample!" It's weird in that you can't really "sample" it right away, but it smells nice and gives you a first-hand look at their quality and hopefully lures you in.
I would urge you to be playful as a seller. Make eye contact, smile a lot, don't be afraid to talk loud, and say, "Good day, m'lord" and "Good day, m'lady." Faires are incredibly fun when everyone is playing and incredibly awkward when some people won't play/interact.
And if you learn to make authentic 16th century handfans, please PM me - I'm redoing my garb (costume) and am in the market for a fan!